1. Field of the Invention
The present invention relates to a method and an apparatus for detecting foreign matter of a sheet material formed through, for example, calendering processing.
2. Description of the Prior Art
When the surface of a sheet material formed through calendering processing or the like is covered with a film made of polyethylene or the like, the film has been removed from the sheet material before starting the sheet-material winding step.
However, because the film has a large adhesion, the film is easily cut when the film is removed from the sheet material. If a residual film is left on the sheet material, a trouble occurs in the winding step. Therefore, presence or absence of a residual film has been visually inspected. However, when a film is attached to at the lower side of a sheet material, in a sheet-material carrying line, it may be difficult to find a residual film and thereby, a problem occurs that a reliable inspection cannot be performed. Moreover, because of visual inspection, problems occur that personnel cost for visual inspection increases or operability lowers.
The present invention is achieved to solve the above problems and its object is to provide sheet-material foreign-matter detecting method and apparatus capable of securely detecting foreign matter attached to a sheet material.
The present invention uses a sheet-material foreign-matter detecting method for detecting whether foreign matter different in reflectance from a sheet material having light reflectivity is attached to the surface of the sheet material while moving the sheet material in a predetermined direction, in which a difference between brightnesses of a reflected image of a light source due to a difference between reflectances of the sheet material and the foreign matter is judged by applying light to a predetermined position of a moving route of the sheet material from a position having a predetermined angle against the surface of the sheet material and picking up a light-source image reflected to the surface of the sheet material by image pickup means.
Thereby, because brightnesses of the light-source reflected image picked up by the image pickup means are different from each other when the foreign matter is attached to the sheet material and when the foreign matter is not attached to the sheet material, the attached foreign matter is detected in accordance with the difference between brightnesses of the reflected image. Therefore, it is possible to always perform a reliable inspection and moreover, automate inspections because foreign matter attached to a sheet material can be securely detected, resulting in an advantage without any personal cost increasing and operability lowering.
Moreover, as for the above method, the light-source reflected image is picked up at a position shifted by a predetermined distance along the surface of the sheet material from a light reflected position along the optical axis of the light source.
Thereby, because a position for picking up the light-source image reflected to the sheet material is shifted from the light reflected position along the optical axis of the light source, a reflected image having a brightness lower than that of a reflected image formed by direct light along the optical axis is detected and a difference between brightnesses of a reflected image due to presence or absence of foreign matter becomes clear. Therefore, it is possible to improve a detection accuracy.
Moreover, it is possible to realize an apparatus having the above functional effect by configuring a sheet-material foreign-matter detecting apparatus for detecting whether foreign matter different in reflectance from a sheet material having light reflectivity is attached to the surface of the sheet material while moving the sheet material in a predetermined direction, by a light source for emitting light to a predetermined position of a moving route of the sheet material from a position having a predetermined angle from the surface of the sheet material, an image pickup means for picking up the light-source image reflected to the surface of the sheet material, and a judging means for performing judgement in accordance with a difference between brightnesses of the light-source reflected image due to a difference between reflectances of the sheet material and the foreign matter.
Moreover, in the above configuration, by shifting a position for picking up the light-source reflected image in the sheet material by a predetermined distance from a light reflecting position along the optical axis of the light source, it is possible to clarify a difference between brightnesses of a reflected image due to presence or absence of foreign matter similarly to the above description.
Furthermore, in the above configuration, by configuring the judging means by image processing means for image-processing the data picked up by the image pickup means and detecting whether the brightness of a predetermined area of processed images including the light-source reflected image becomes a predetermined value or less, the brightness of the predetermined area including the light-source reflected image which is image-processed is judged. Therefore, the brightness is not influenced by light reflected from areas other than the predetermined area. Therefore, it is possible to further improve a detection accuracy.